1. Field of the Invention
The present invention relates to an endoscope and an endoscope system and specifically relates to an endoscope and an endoscope system that perform processing for adjusting sampling timings in correlated double sampling.
2. Description of the Related Art
Conventionally, endoscopes have widely been used in medical and industrial fields. An endoscope system includes an endoscope that includes an elongated insertion portion, and a body portion, and picks up an image of an object by means of an image pickup device provided in a distal end portion of the insertion portion, and processes the image pickup signal in an image processing section of the body portion, and displays an image of the object on a monitor. The image pickup device includes, for example, a CCD, and is driven by a drive signal to output an image pickup signal.
In the endoscope system, in order to remove noise in an analog image pickup signal from the image pickup device, correlated double sampling is used. Correlated double sampling processing is processing for sampling an output signal from the CCD via a feedthrough sampling pulse and a clamp pulse and taking difference between the two signals obtained by the sampling to remove, e.g., reset noise. A correlated double sampling circuit (hereinafter referred to as CDS circuit) is provided in the body portion to which the endoscope is connected or the endoscope itself.
Also, since the lengths of the insertion portions of endoscopes are different depending on the types of endoscopes, the time consumed for an image pickup signal received in response to a drive signal from a drive circuit to reach a CDS circuit is also different. Thus, it is necessary to adjust timings for sampling the received image pickup signal.
For example, at the time of manufacture, the cumbersome work of connecting a measuring device that measures a signal waveform to a signal processing circuit in the body portion, and an adjuster for the circuit manually making, i.e., adjustment of a delay amount in a delay circuit is required for sampling timing adjustment.
Therefore, methods in which a reference signal having predetermined amplitude is generated from an output signal from a CCD and phase adjustment is automatically made based on the reference signal such as disclosed in Japanese Patent Application Laid-Open Publication No. 2001-340290 or 2002-27335 have been proposed.
Also, there is a method in which a signal for sampling is automatically generated from a clock signal superimposed in a blanking period of an output signal from a CCD, using a PLL circuit.